Arrangement for maintaining optimum minimum operating clearance between rotor and stator components of fluid-flow machines and the like

ABSTRACT

Between the rotor and stator components of turbo-machines, compressors, pressure wave machines and the like, the clearance space is partially filled out by an abradable element which is capable of &#34;growing&#34; when subjected to an elevated temperature and/or to the influence of the particular atmosphere in which the machine operates. As the element grows, it compensates for corrosion and erosion factors which take place in the machine and which otherwise tend to increase the clearance. Suitable materials which will &#34;grow&#34; under these operating conditions are gray cast iron and a sintered graphite-metal.

CROSS-REFERENCE TO RELATED CASE

This application is a continuation application of my commonly assignedUnited States application Ser. No. 700,449, filed June 28, 1976, nowU.S. Pat. No. 4,083,650, granted Apr. 11, 1978 which, in turn, is acontinuation application of my commonly assigned, co-pending UnitedStates Application Ser. No. 483,076, filed June 25, 1974, now abandoned,and entitled "Arrangement for Maintaining Optimum Minimum OperatingClearance Between Rotor And Stator Components of Turbo-Machines,Compressors, Pressure Wave Machines and The Like".

BACKGROUND OF THE INVENTION

The present invention relates to an improved technique by means of whichthe necessary operating clearance between the rotor of a machine and itsassociated stator component can be maintained at a safe minimum therebyto maintain an optimum efficiency of operation during the life of themachine.

The invention is applicable to various types of machines incorporatingrotor and stator components such as for example various types ofturbines, compressors and pressure wave machines, an example of thelatter being disclosed in U.S. Pat. No. 3,591,313, granted July 6, 1971to Alfred Wunsch.

The efficiency of such manchines is determined by various factorsincluding the size of the operating clearance between the rotor andstator and will decrease as the clearance increases. For this reason,efforts are being continuously made to reduce the clearance as much aspossible without, however, incurring potential damage to the machineryas would be caused by accidental touching of the stator by the rotor.The optimum amount of the necessary operating clearance is determined onthe basis of the properties of the materials involved, manufacturingtechnology, the size of the rotor and stator and also the operatingconditions of the machine. Care must also be taken that in exceptionalcircumstances, whenever the rotor touches the stator, that damage willnot occur. Such exceptional circumstances may arise, for example, duringthe starting-up period of the machine, or in the event of strongvibrations occuring during operation, or excessive increases in machinetemperature and the like.

It has been proposed, for example, in the case of turbo-machines andcompressors, to provide the tips of the rotor blading with a bevelledsurface in order to keep the operating clearance between the blading andthe surrounding surface of the stator to a minimum. In the event thatthe tips of the blades touch the stator surface, the bevelled blade willdeform, or wear down, and no harmful forces will be generated.

It has also been proposed, in order to establish a minimum clearance, tocoat the walls of the stator at their inner surface opposite the rotorwith a relatively soft layer which can be abraded away or deformed byany accidental touching of the tips of the rotor blading. Such softlayers can consist, for example, of graphite, die-cast or sinteredporous nickel-chromium alloys, or nickel-graphite materials, honeycombedcells, etc. and are called abrasable layers for touch protection. Allprotective layers of this type are lacking in the property to "grow"i.e., to increase in size, under the influence of the environmentaltemperature and/or the particular atmosphere in which the machineoperates.

These know expedients have the disadvantage that the bevelled blade endsor soft layers will change their shape irreversibly upon contact, eitherby deforming or wearing down. In addition thereto, the blade ends, inthe case of turbo-machines and compressors, or the ends of the cellwalls, in the case of pressure wave machines, as well as the stator willbe subjected to corrosion and erosion, with the result that theoperating clearance as between rotor and stator will increasecontinuously and the efficiency of the machine will decrease in acorresponding manner.

SUMMARY OF THE INVENTION

The principal object of the present invention is to maintain theoperating clearance between the rotor and stator at a safe minimum evenin the case of operations lasting for long periods of time.

This objective is attained in that within the region of the clearance,there is utilized an abrasive or abradable material that will "grow",i.e., increase in size and which is brought about by the operatingtemperature and/or working atmosphere of the machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concepts will be further explained in further detail asapplied to different types of machines and as illustrated in theaccompanying drawings wherein:

FIG. 1 is a sectional view showing a portion of the rotor and stator ofa compressor as improved by the invention;

FIG. 2 is a sectional view of a portion of the rotor and stator of apressure wave machine;

FIG. 3 are graphs plotting the "growth" characteristic of two differentabradable sintered graphite-metal alloys that can be used inestablishing the region of clearance as between rotor and statorcomponents of a machine;

FIG. 4 are also graphs plotting the "growth" of three different types ofabradable gray iron alloys that can be used in establishing theclearance region; and

FIG. 5 is a sectional view of a portion of the rotor and statorcomponents of another pressure wave machine.

DETAILED DESCRIPTION OF THE INVENTION

With reference now to FIG. 1, which shows a section of an axial cutthrough a compressor, there is provided the stator component 1, therotor 2 and the rotor blading 3. The stator and rotor are made of avolume-stable material, for example, steel. In order to maintain thedistance 4 between the ends of the rotor blading 3 and the stator 1 assmall as possible, there is secured at the internal surface of thestator 1 opposite the blade ends a segmented ring 5 and which is madefrom one of the abradable materials heretofore referred to as beingcapable of "growing", preferably gray cast iron. In the event that thetips of the blades 3 touch the segmental ring 5, they will becomedeformed if they are bevelled, or the segmented ring 5, if soft willbecome eroded on the rotor side. Due to, for example, the oxidizingatmosphere in which the compressor works on the one hand, and theoperating temperature of the compressor on the other hand, or both, thering 5 will irreversibly "grow" in the radial direction towards therotor axis thus reducing the clearance 6 that has been accidently causedto increase by the unforeseen touching and corrosion-erosion effectheretofore referred to. In this manner, there is compensated out thecorrosion- and erosion-degradation, as well as the wear caused byunforeseen vibrations and temperature increases. Thus the segmental ring5 by its growth serves as a self-compensating member to maintain theoperating clearance at an optimum minimum thereby achieving a continuousoptimum efficiency over a long period of operating time of the machine.

In FIG. 2, the teachings of the invention have been illustrated asapplied to a pressure wave machine of the general type more completelydisclosed, for example, in the above-referred to U.S. Pat. No.3,591,313. The stator component 7 of the machine is made from cast ironwith spheroidal graphite and its rotor 8 is made from a nickel alloy. Inorder to maintain the distance 9 between the front end of the celledrotor 8 and the stator 7 as small as possible a plate 12 is cast intothe stator 7 so as to face the end of the rotor. Plate 12 is made froman abradable material capable of growth, preferably soft gray iron.Thus, here again, the plate 12 will "grow", i.e., increase its volume inthe axial direction towards the end of rotor 8 as a result of anoxidizing working atmosphere handled by the machine, on the one handand/or by the operating temperature of the machine, on the other hand.Thus, the clearance 10 will be maintained at an optimum minimum value.

The embodiment illustrated in FIG. 2 can be modified by securing plate12 to the front end of rotor 8 rather than to the stator so that plate12 will "grow" in the direction of the rotor axis towards stator 7,thereby achieving the same result. In principle, it is thus feasible toaffix such a self-compensating growth of growable component to the rotorand/or the stator. Since the rotor parts are usually subjected to heavymechanical stresses it will be expedient to provide only the statorcomponent with the necessary growable element.

If, in the embodiments illustrated in FIGS. 1 and 2, no unexpectedcircumstances arise and no wear occurs, so that the growth of thesegmented ring 5, or of plate 12, respectively will become greater thanthe abrasive wear-down effect caused by corrosion and erosion, the partswill be worn down gradually by the rotor, with the result that theclearance 6, as in FIG. 1, or clearance 10 as in FIG. 2, will always bemaintained at a minimum.

The growth characteristics of three different types of gray cast ironare plotted in FIG. 4, in relation to annealing time in hours at an airtemperature of 650° C. Plot "a" is for a gray cast iron containing 3.7%carbon, 2.6% silicon, (78HB). Plot "b" is for a gray cast ironcontaining 3.3% carbon, 5.9% silicon, (131HB). Plot "c" is for a graycast iron containing 3.3% carbon, 6.5% silicon, (149HB).

The "growth" characteristic of the gray cast iron which is utilized forthe manufacture of the segmented ring 5 or plate 12, can be variedwidely, for example, by proper selection of its components, by variationof the cooling speed during casting of the iron, by thermal treatment ofthe iron after casting, and so forth.

Furthermore, the growth of the segmented ring 5 or plate 12 producedfrom the gray cast iron is influenced by its shape, the type offastening to the base material, by its stress, and by the operatingtemperature and type of atmosphere in which the machine operates.

It is also possible to use for the manufacture of the segmented ring 5and plate 12 abradable cast iron types other than gray cast iron, suchas malleable cast iron, cast iron with graphite, partially, in globularand partially in lamellar form, and so forth, dependent upon thecharacteristics desired for the growable element.

The growable elements are secured to the supporting base material of thestator or of the rotor by standard methods, mechanically, or bysoldering, welding, casting, sintering and so forth.

The growable elements also can be made from abradable materials otherthan cast iron, i.e., materials which will grow by oxidation at highertemperatures. Particularly suitable are sinteredgraphite-metal-materials, their metal phase containing nickel, copper,iron, tin, lead, antimony and/or zinc. The two different graphs plottedin FIG. 3 in which growth is plotted in relation to annealing time inhours in air at a temperature of 350° C. show that the growth will befaster if the metal phase contains a greater amount of readilyoxidizable components such as copper and tin. Plot "a" is for a sinteredmaterial containing, by weight, 8% carbon, 55% copper, 28% nickel and 9%iron. Plot "b" is for a sintered material containing, by weight, 8%carbon, 78% copper, 12% tin and 2% nickel.

In principle, it is possible to use for the manufacture of the elements5 and 12 any abradable material that will "grow" under the influence ofchemical elements, or in combination with the environment, for example,by carburization, nitriding, sulphurating, oxidation and the like, or bya change in structure under the influence of the operating temperature.

If it is desired to keep the forces generated by touching of the rotorand stator parts to a very low value, it is possible, in the case of thetwo different embodiments of the invention which have been describedherein, to apply to the rotor side of the growable element 5 or 12respectively, an additional, known soft protective layer as previouslydescribed which will abrade off with ease.

The embodiment of the invention as illustrated in FIG. 5 is similar tothat of FIG. 2, namely a pressure wave machine and hence the samenumerals have been used to designate those parts which are common toboth. The construction according to FIG. 5 differs from that of FIG. 2in that the front end cover plate 11 of the stator 7' and plate 12' havebeen integrated into a single structure and which is made from amaterial, preferably gray cast iron, which will grow under the influenceof the particular atmosphere or temperature at which the pressure wavemachine operates. A "separation" as between the cover plate portion 11and plate 12' is shown symbolically by a dash-dot line. Any growth ofthe cover plate portion can be prevented, for example, by locatingcooling coils 13 within this portion, thus assuring a continuous lowoperating temperature thereof. Here again, it is possible to place onone, or both of the front sides S2,S1 of the plate portion 12' and theend of the rotor 8', respectively, protective layers, as described,which will abrade off with ease.

While there are shown and described present preferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited hereto, buy may be otherwise variously embodied and practicedwithin the scope of the following claims. ACCORDINGLY,

What I claim is:
 1. In a machine operating under varying operatingconditions and which incorporates rotor and stator components andwherein a space is provided intermediate a surface of the rotor and anoppositely located surface of the stator thereby to define an operatingclearance therebetween for the rotor, the improvement comprising anabradable element interposed in said space and partially filling thesame, said abradable element constituting a growth element compensatingfor its own growth or wear in order to maintain said operating clearanceat a size promoting efficient operation of the machine throughout itsvarying operating conditions, and said growth element growingirreversibly under the operational conditions of the machine to therebycompensate for repeated abrasion or wear to which said growth element issubjected to during operation of the machine throughout its veryingoperating conditions.
 2. In a machine which incorporates rotor andstator components and wherein at least one abradable sealing element isprovided intermediate a surface of the rotor and an oppositely locatedsurface of the stator thereby to define an operating clearancetherebetween, the improvement that said abradable element consists of asintered graphite-metal composition and that the metal phase of saidcomposition contains at least one element of the group consisting ofcopper, tin, lead, antimony and zinc together with at least one elementof the group consisting of nickel and iron, said abradable elementconstituting a growth element compensating for its own abrasion or wearin order to maintain said operating clearance at a size promotingefficient operation of the machine and said growth element growing underthe operational conditions of the machine to thereby compensate forabrasion or wear to which said growth element is subjected to duringoperation of the machine.